wrocesses operate in the uptake ant: (1) a direct transfer of ionic hydrosphere to the organism, neluding adsorbed surface ions. es of the specificity of metal ions re and properties. Manyof these of the specificity of metal ions e.g. (1) mass, (2) ionic charge, ential, (5) the configuration and in solution, and (6) the configurof the metallic ion with substanbottom clays and muds). closely related, since they are periodical table; thus they differ i-reduction potential or mobility, forming coordination complexes iay form either ionic or covalent + form aquocations of the type all may form coordination comthe other transition metal ions spect than Mg, since the unfilled alent as well as essentially ionic bonding) of general importance md, which results from electrorarged metal ion and a dipolar ranging from the simple aquonetal ions to form such complexes spt for the ions of the transition s out of proportion to their ionic as Cst, Rb+ and K+ show the xxes. Those of somewhat higher show intermediate activity. ve in forming coordination commtially covalent linkages between ; well as ionic complexes. This of the first transition series have - molecules to fill out their 3-d valent linkages in which a pair the group bound. Thetransition dwever, many coordination comthe bond must be regarded as a types (16). lements with any given biological upon the chemical composition irs in the following order: <Cutt+ >Zntt. lation of the trace metal ions, nique when compared with other transport mechanisms. The transition elements were taken up by cells from a solution of very low concentration of the metals without apparent expenditure of energy by the cells, and was thus a non-metabolic process. Neither did the process obey the laws of diffusion normally observed for other elements, in that they did not respond to concentration gradients. Saltman concluded that for the transition elements no diffusion barrier was presented by the cell membrane, but that the rate of uptake was limited by the rate at which the ions found binding sites inside the cell. This process would exert only a minor effect on the external surfaces of planktonic organisms, but would be of major importance where cell surfaces were exposed. Korrinea (18) noted that oysters and other lamellibranchs concentrated considerable quantities of the metals Al, Mn, Fe, Cu, Zn and Pb, especially during periods of active feeding, although they occurred in very small concentrations in the environment. Korringa stated that the electrical properties of the food particles and the mucus feeding sheets in the oyster determine whether or not particles are rapidly caught. The positive polyvalent ions such as Alt+*++, Cut+, Fe++, Zn++, Hg++ and Mn++ were observed to be caught and accumulated by the oyster, but not positive monovalent ions such as Na+ and K+, though present in greater amounts. The ability of plankton organisms to form complexes with heavy metal anions and the transition elements is illustrated by observations on the uptake of radiocelements by these organisms in areas of radioactive fallout. The levels of different radioisotopes in plankton change with time after introduction of contamination. The change in ratio depends upon at least two main factors—the physical decay of the radioisotopes in question, and the velocity at which concentration of the individual isotopes occurs within the organisms. During the first 48 hours after detonation the principal isotope present in the plankton was Np??? (69 °%, Table 1). Mo®®9—Tc®*™ and Te1#*—[)% contributed approximately 10°, each of the total activity. [/52 was the only iodine radioisotope found in measurable amount in marine plankton, and -was present only as a consequence of being the daughter of Te!*?. Radioactive iodine would be in solution in sea-water and, unless taken up selectively, would undergo dilution by stable chlorine, bromine and fluorine, as well as isotope dilution by the stable iodine. Other isotopes present in plankton within the first 48 hours after contamination at levels of 3°, or less included U23", radioactive Ru-Rh, Ce-Pr, Ba-La, and Zr-Nb. Thus the radioisotopes associated with the plankton during the first 48 hours consisted principally of radioactive anions (96%). Later than one week after contamination the ratio of the different isotopes in the plankton changed so that only 15% of the total radioactivity was contributed by the anions—Zr°5—Nb*®, 6%; radioactive Ru—Rh, 5%; Np?99, 2% and U?37, 27. At this time Co5’. 58, 60 contributed 43°, of the total radioactivity; Zn®> accounted for 3°, and Fe*5+59 for 16%. Bat40—La}4° contributed the remaining 23%. In samples collected six weeks after detonation in 1956, the major isotopes were Zn*® (25%), Fe®> (24%), and Co%. 8, 60 (24°). Most of the remaining activity was contributed by Zr°®°—Nb®> (20%), Cet#4—Pri44 (5%), and Rul$—Rh1 (1.4%); Mn*4 was present only in trace amounts. Therefore the initial uptake of radioisotopes by plankton included, for the most part, short-lived radioactive anions. However, within a short time the radioactive transition elements cobalt, zinc, iron and manganese were accumulated and retained by plankton, so that at an interval greater than 121